1. Field of Invention
The invention generally relates to a liquid crystal lens, and more particularly to a liquid crystal lens with a preferable optical imaging characteristic.
2. Description of Related Art
FIG. 1 is a schematic view of a conventional liquid crystal lens. Referring to FIG. 1, a liquid crystal lens 100 includes a first substrate 102, a first electrode layer 110, a liquid crystal layer 120, a second electrode layer 130, and a second substrate 104 stacked in sequence. An alignment layer 140 and an alignment layer 150 are disposed between the liquid crystal layer 120 and the first and second substrates 102 and 104, respectively, so that a liquid crystal molecule 122 in the liquid crystal layer 120 has a predetermined alignment direction. Typically speaking, the second electrode layer 130 has an opening H located at a center of the liquid crystal lens 100.
When using the liquid crystal lens 100, the liquid crystal molecule 122 in the liquid crystal layer 120 tilts according to an electric field direction, for example through a signal source S applying a voltage signal to the first and second electrode layers 110 and 130. Since the opening H is located at the center of the liquid crystal lens 100, a center region of the liquid crystal lens 100 has a weaker electric field intensity, and an edge region of the liquid crystal lens 100 has a stronger electric field intensity. Accordingly, a non-uniform electric field variation is formed between the first and second electrode layers 110 and 130. Moreover, the liquid crystal molecule 122 in the liquid crystal layer 120 produces a different degree of tilt according to the electric field variation, so that the liquid crystal layer 120 produces a step-wise variation of a refractive index. For example, when a light beam L passes through the liquid crystal lens 100, the light beam L generates a light condensing effect due to the refractive index variation of the liquid crystal layer 120, and the light beam L is concentrated on a focus F depicted in FIG. 1.
However, the step-wise variation of the refractive index in the liquid crystal lens 100 still significantly differs from a typical optical lens. In other words, the conventional liquid crystal lens 100 cannot achieve an optical imaging characteristic of a typical lens.